This invention relates to an electrostatographic printing machine, and more particularly concerns an apparatus for separating a sheet of support material from a heated fuser member employed in the printing machine.
In a typical electrostatographic printing machine, a latent image is recorded on a surface and developed with charged particles. After the latent image is developed, a sheet of support material is positioned closely adjacent thereto so as to receive the particles therefrom. The particles are then permanently affixed to the sheet of support material forming a copy of the original document thereon. Electrographic and electrophotographic printing are differing versions of electrostatographic printing. The process of electrophotographic printing employs a photoconductive member arranged to be charged to a substantially uniform level. The charged photoconductive member is exposed to a light image of an original document. The light image irradiates the charged photoconductive member dissipating the charge in accordance with the intensity of the light transmitted thereto. This records an electrostatic latent image on the photoconductive surface. Electrographic printing differs from electrophotographic printing in that neither a photoconductive member nor a light image of the original document are required to create a latent image on the surface. Both of the foregoing processes generally employ heat settable particles to develop the latent image. The particles are permanently fused to the sheet of support material by the application of heat thereto.
Various techniques have been developed for applying heat to the particles on the sheet of support material. One technique is to pass the sheet of support material with the powder image thereon through a pair of opposed rollers. In one such system, a heated fuser roll and a non-heated backup roll are employed.
In the most commonly employed type of heated roll fuser, the heated fuser roll has the outer surface thereof covered with a polytetrafluorethylene commonly known as Teflon to which a release agent such as silicone oil is applied. The Teflon layer, preferably, has a thickness of about several mils.
Teflon coated fuser rolls of the type discussed above have been found unsuitable for fusing high powder height toner images such as those formed in a color printing process such as will be discussed hereinafter. Accordingly, an alternate approach to fusing toner images by means of a heated roll system comprises utilization of a of metal heated roll which has a low molecular weight polyethylene applied thereto as a release agent. While such a roll construction satisfactorily fuses the toner images formed during a color reproduction process utilizing different colored toners, it has been found that conventional stripping means such as individual stripping fingers do not satisfactorily strip the copy paper from the heated fuser roll member.
Accordingly, it is the primary object of the present invention to improve the apparatus employed to separate the sheet of support material from the fuser member utilized in a color copier of the xerographic type.